Metal-Mediated, Completely Diastereofacial Conjugate Addition of Trialkylstannylmetal Reagents to γ-Alkoxy-α,β-Unsaturated Esters.

Complete control of the face of attack in the addition of stannylmetal reagents to γ-alkoxy-α,β-unsaturated esters can be achieved by using the appropriate counterion (see scheme). The stereochemistry of addition does not depend on the configuration of the C-C double bond, although the stereoselectivity is consistently better with the Z stereoisomer, for which 100 % Si attack is obtained with Li as counterion and 100 % Re attack with LiZnEt.